JP2017022985A - Operation of wind turbine based on frequency of ac output voltage signal supplied by power converter of wind turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate a wind turbine on the basis of a frequency of an AC output voltage signal supplied by a power converter of the wind turbine.SOLUTION: A wind turbine 120 includes mechanical drive trains 222 and 228, a power generator 230 mechanically connected to the drive trains, and a power converter 240 electrically connected to the power generator. A method for operating the wind turbine includes the steps of: a) calculating a frequency of the AC output voltage signal supplied by the power converter; b) determining whether the calculated frequency significantly changed more than a prescribed threshold value with respect to the previously calculated frequencies; c) changing a power reference signal for the wind turbine when change in the calculated frequency is larger than the prescribed threshold value; d) supplying the changed power reference signal to a controller 250 of the wind turbine; and e) controlling the operation of the wind turbine on the basis of the changed power reference signal.SELECTED DRAWING: Figure 2

Description

  The present invention generally relates to the technical field of transmitting electric power generated by a wind park including a plurality of wind turbines from the wind park to an electric power system. In particular, the present invention relates to a method for operating a wind turbine that can efficiently transmit power from a wind park including the wind turbine to a power system. The invention further relates to a wind turbine capable of implementing such a wind turbine control method and a method for controlling the overall power generation of a plurality of wind turbines in one wind park, wherein each wind turbine is A wind turbine control method can be implemented.

  As used herein, the term “wind park” refers to any arrangement that includes at least two wind turbines that generate power commonly supplied to a power system. A “wind park” is sometimes called a “wind farm” or, more simply, a “wind power plant”. The wind park may be arranged offshore or onshore.

Background Art Wind turbines are used to convert mechanical wind energy into electrical energy in a clean and efficient manner. In the case of a wind turbine, the generator is driven directly or via a gearbox by a mechanical drive train having a rotor with a plurality of rotor blades. The resulting alternating current (AC) frequency at the generator stator terminal is directly proportional to the rotational speed of the rotor. The voltage at the stator terminal also varies depending on the rotational speed of the generator. For optimum energy acquisition, this rotational speed varies depending on the speed of available wind driving the rotor blades. The rotational speed of the generator can be controlled by changing the pitch angle of the rotor blades to limit energy acquisition at high wind speeds and to avoid possible damage to the rotor.

  Matching the generator variable voltage and frequency to the power system voltage and frequency, which is nominally constant, is generally accomplished by a power converter. Power converters typically include a generator-side bridge that operates during normal operation as an active rectifier that provides power to a direct current (DC) link. The generator-side bridge can have any suitable topology with a series of semiconductor power switching devices that are fully controlled and tuned using a pulse width modulation (PWM) strategy. In addition, the power converter generally has a system side bridge, which converts the DC power of the DC link into AC power that is matched to the individual electrical quantities of the power system with respect to voltage, frequency and phase angle. Convert to When transmitting or transmitting power from a system side bridge or from a bus bar connected to a plurality of system side bridges (eg, via one transformer each), in addition to the voltage amplitude, at the output of the system side bridge, or The relative phase of the voltage signal at the bus bar relative to the phase of the power system is also an important value regarding how much power can be transmitted.

  In this regard, such a phase angle is associated with a predetermined back electromotive force (back EMF), and according to another approach to explain power transfer, such a back electromotive force is Is required to transmit power to the power grid. According to this approach, the back electromotive force is formed by the power system.

  However, in contrast to AC power connections, in particular, the power generated by a plurality of wind turbines belonging to one wind park can also be transmitted to the power system via so-called high voltage direct current (HVDC) power connections. Is possible. Such a solution is particularly suitable for offshore wind parks where the distance between a) one wind turbine and b) individual onshore power systems is long (eg several hundred km). When the distance is long, the power loss in the high voltage DC transmission system is significantly smaller than the corresponding loss in the AC transmission system. This is because, in the case of an AC power transmission system, inductive power loss due to parasitic inductance of individual cables is particularly large.

The following describes transmission from an offshore wind park to an onshore power system via a high voltage DC transmission system:
1) Each of a plurality of offshore wind turbines (including power converters each having a generator side (AC / DC) bridge, a DC link, and a system side (DC / AC) bridge) generate medium voltage AC power . Each medium voltage AC power is collected at the first bus bar.
2) Medium voltage AC power collected at the first bus bar is converted to high voltage (HV) AC power through a transformer constructed offshore at the substation.
3) High voltage AC power and other high voltage DC power from other substations are collected at the second bus bar and supplied to the high voltage DC facility as common high voltage AC power, This common high voltage AC power is converted to DC power.
4) DC power is transmitted onshore via a (low loss) high voltage DC cable that can be somewhat longer than 100 km.
5) Onshore, DC power is supplied to a (DC / AC) converter station, which generates a modulated AC power output.
This AC power output signal is supplied to the onshore AC power system at an appropriate voltage and an appropriate frequency or phase angle.

  In this regard, the high voltage DC cable, when compared to the AC power system in terms of inductance, only forms a significantly weaker power receiver, and this is also the effective back electromotive force required to receive power. Can not supply. Therefore, in order to enable efficient power transmission, the system side (DC / AC) bridge of the wind turbine must be operated so that the required back electromotive force is generated.

  In a high voltage DC facility, a high power AC / DC converter can be used to convert common high voltage AC power to DC power (see item 3 above), which includes a total of 6 Power semiconductor switches are included, where each two power semiconductor switches each extend between two DC output terminals of a high power AC / DC converter (of three) one half They are connected in series in the bridge path. The power semiconductor switch can be driven by pulse width modulation (PWM) as is well known. The advantage of such AC / DC conversion is that bidirectional power flow is possible by setting an appropriate switching pattern. However, a drawback of such AC / DC conversion is that a high-power AC / DC converter is a complex, large, and extremely heavy object. Also, air insulation must be provided for reliable operation.

  Another recently proposed approach for AC / DC power conversion in high voltage DC facilities is an approach based on the concept of a rectifier with six passive high power diodes. Also in this case, two high power diodes are connected in series in one half bridge path (out of three) extending between the two DC output terminals of the corresponding power rectifier. The advantage of this approach is that the rectifier can be realized as an encapsulated device in a simple and robust manner. The power loss in the rectifier is small and relatively little maintenance cost is required for rectifier operation.

  However, the drawback of such a “rectifier approach” is that only one-way power flow is possible. When power must be transmitted from the onshore power system to the wind park, a so-called umbilical AC cable that extends in parallel with the high voltage DC power cable is connected between the onshore power system and the wind park. Must be equipped in the system. Transmission over umbilical AC cables is necessary, for example, during the start-up phase of at least some wind turbines in the wind park, when the power generation of other wind turbines is insufficient to allow reliable start-up It may be said. Yet another attempt when using a (passive) rectifier is to determine the amplitude, frequency and phase of the common high voltage AC power to be rectified, exclusively the DC of each individual wind turbine. / It shall be controlled by the AC system side bridge.

  In this case, it is possible to supply power to the wind park when necessary from a local power source in addition to the umbilical AC cable. Such local power sources can be power storage devices, generators, fuel cells, compressed air, heat storage devices, or pumped storage, or possible combinations of various power sources.

Summary of the Invention In this case, it is considered necessary to control the characteristic amount of high voltage AC power to be converted to high voltage DC power in the high voltage DC transmission system.

  This problem can be solved by the invention described in the independent claims. The dependent claims contain advantageous embodiments of the invention.

According to a first aspect of the invention, there is provided a method for controlling the operation of a wind turbine comprising: i) a mechanical drive train; and ii) mechanically connected to the drive train. A generator, and iii) a power converter electrically connected to the generator. The method provided here includes the following steps: That is,
a) determining the frequency of the AC output voltage signal supplied by the power converter;
b) identifying whether the determined frequency has changed more than a predetermined threshold with respect to the previously determined frequency;
c) changing the power reference signal for the wind turbine if the determined change in frequency is greater than a predetermined threshold;
d) supplying the modified power reference signal to the wind turbine controller;
e) controlling the operation of the wind turbine based on the modified power reference signal.

  The idea on which this aspect of the invention is based is that a given point or node in a power grid that connects a wind turbine, in particular a plurality of wind turbines of a wind park, with a power grid (often called a grid). The frequency imbalance is caused by the power imbalance that can occur at the location. When detecting or monitoring such a frequency, if it is identified that this frequency has changed to or within a predetermined range, the power reference signal can be changed or adjusted in an appropriate manner. Such power imbalance can be at least partially reduced. In particular, the power generation of the wind turbine is increased if it is identified that the frequency has been drooped or lowered at least to a predetermined range or to a predetermined range. As long as sufficient wind is available, this is accomplished in a known manner by increasing the power reference signal. Conversely, if it is identified that the frequency has increased at least to a predetermined range or to a predetermined range, the power generation of the wind turbine is reduced. This is achieved by reducing the power reference signal.

  According to the above-mentioned method, it is often called a High Performance Park Pilot (HPPP) controller and requires coordination using a higher-level wind park controller that is only possible with relatively slow control. The power generation of the entire wind park can be coordinated by a method of automatically coordinating without returning to the coordinated state. In particular, coordinated control of the entire wind park can be achieved effectively without the need for any control information exchange between individual wind turbines. According to this concept, each wind turbine operates as an individual independent entity, but operates in a way that is responsible for at least partially achieving the power balance adjustment represented by the normalized frequency.

  In other words, this will be explained. Under normal conditions, the wind turbine can autonomously control its active power output like a conventional wind turbine control procedure. And according to one embodiment of the present invention, the wind turbine can make autonomous decisions based on local measurements and / or derivations, as well as the rest of the wind park that makes autonomous decisions. The reaction is performed in a predetermined manner coordinated with the wind turbine.

  The frequency of the AC output voltage signal can be determined a) by voltage measurement at the terminal of the wind turbine and / or b) directly derived from internal control variables for the power converter. In the latter case, the frequency can be obtained from the angular velocity of the rotation reference frame, for example. This rotation reference frame is applied as part of a strategy for controlling the operation of the semiconductor switch of the DC / AC system side bridge in the power converter for the purpose of generating an AC output voltage.

  When determined from the internal control variables of the power converter, all or selected contributions of the various contributions to the angular frequency of the AC output voltage signal are used to achieve the desired performance / target in wind turbine operation. Can be used.

  According to the presently preferred embodiment of the present invention, the frequency of the AC output voltage signal is derived from the output of the wind turbine power controller or is indirectly determined. According to this, the power error signal is converted to frequency, which can be understood as a normal reaction of synchronous matching to the power (control) error signal. In contrast to measuring the AC output voltage (as is) to determine the AC output voltage signal, the use of the power error signal provides the advantage that the individual motion control will include a delay. Can do. As a result of such delays, the overall performance is typically degraded and in some cases stability problems may occur.

  In the context of the present specification, the term mechanical drive train is used for all mechanical components of the wind turbine provided to mechanically drive the generator rotor. Particularly for the drive train, a wind turbine rotor, preferably having three rotor blades attached to the hub, and a rotatable drive that connects the hub directly or indirectly to the generator rotor, for example via a gearbox. Axis.

  According to one embodiment of the present invention, the frequency is determined at one node of a power transmission system that connects the power converter to the power system. In this case, the power transmission system has a high voltage direct current (HVDC). Consists of transmission lines.

  When high-voltage direct current power transmission is used, the power balance control described above according to the frequency (monitored) is particularly advantageous. This is because, as already mentioned in the introductory part of this specification, the high-voltage direct current part of the transmission system only forms a significantly weaker power receiver, which is used to send power to the power system. Very little needed back electromotive force is supplied (in the case of a diode rectifier, the back electromotive force supplied is substantially zero). Therefore, as described above, the necessary back electromotive force must be generated by the system side (DC / AC) bridge of the wind turbine. According to the method described above, the operation of the wind turbine, in particular the power converter (DC / AC system side bridge) can be controlled easily and reliably so that the necessary back electromotive force is supplied. become.

  In this connection, the power system is generally an AC power system. Of course, this means that it is necessary to install a DC / AC power converter at the end of the high voltage DC transmission line assigned to the AC power system. Thus, the high power DC signal conveyed via the high voltage DC power transmission line is converted into a high power AC signal whose frequency and phase are matched to the AC signal of the AC power system.

  According to another embodiment of the present invention, the high voltage DC transmission system includes a rectifier. An AC / DC converter can also be used basically, which generally includes six power semiconductor switches, but the rectifier is much simpler than such an AC / DC converter. It is a power device, which contains only passive elements, ie high power diodes. As already mentioned, the use of a rectifier offers the advantage that AC / DC conversion can be achieved in a simple and robust manner within the encapsulated device. In this case, the power loss is relatively small and relatively little maintenance costs are required for the operation of the rectifier.

  According to yet another embodiment of the present invention, the high voltage DC power transmission system includes an auxiliary power transmission line, and the auxiliary power transmission line is electrically arranged in parallel with the high voltage DC power transmission line. Connect to the nodes of the power transmission system.

  The connection between the auxiliary power line and the described node may be a direct connection, or alternatively as an indirect connection via one or more other devices in the transmission system. Good. The auxiliary transmission line can in particular be an auxiliary AC transmission line.

The auxiliary transmission line may be considerably weaker than the DC transmission line with respect to the ability to carry large currents or large powers. In particular, the auxiliary transmission line can be used as a so-called umbilical AC cable, which only needs to be used for the following two purposes. That is,
1) AC in case wind park power generation is insufficient to allow at least part of the wind turbine to start up with reliability, eg after periods of no wind or little wind AC power must be conveyed from the power grid to at least some wind turbines.
2) A low-power AC connection between the AC power system and the nodes already described in the transmission system,
a) Power system AC signals that are also used for other transmission systems or other wind parks, generally as a reference to frequency and phase;
b) It can be used to measure the phase angle between the AC signal generated on the wind park side of the power transmission system.

  According to a further embodiment of the invention, the step of controlling the operation of the wind turbine based on the modified power reference signal comprises the steps of a) controlling the operation of the power converter, in particular the direct current of this power converter. / Controlling the operation of the AC system side bridge and / or b) controlling the pitch angle of the blades in the wind turbine rotor of the wind turbine. This can provide the advantage that, as a result of the change of the power reference signal, the power generation changes correspondingly in a simple and reliable manner.

  In order to control the operation of the power converter, a power reference signal can be supplied to the converter controller, which is well known in the art for appropriate pulse width modulation (PWM) for individual power semiconductor switches. In particular, the operation of the DC / AC bridge is controlled.

  In order to control or adjust the pitch angle of at least one blade, a power reference signal can be supplied to the wind turbine controller, which is well known to indicate the current power generation by the power reference signal, as is well known. The pitch angle can be adjusted to at least partially correspond to the required power generation. In other words, by controlling the pitch angle, the entire mechanical wind force or a part thereof converted into electric power can be adjusted in a simple and effective manner.

  According to yet another embodiment of the present invention, the determined frequency change is an increase in the determined frequency value. Furthermore, the predetermined threshold value is an upper limit value that is predetermined for the obtained frequency.

  To explain this, the change in the power reference signal, particularly the reduction in the power reference signal, is performed because the obtained frequency has reached a predetermined upper limit value or intersected with this upper limit value. When

  In this regard, by increasing the frequency of the AC output voltage signal supplied by the DC / AC system side bridge of the power converter, transmission to the AC power system is prevented, or at least significantly reduced or It can be instructed to be reduced. Of great importance in this situation is to reduce power generation very quickly, in particular in order to avoid damage in the wind turbine. Considering the above-mentioned method from the advantages listed here, that is, each wind turbine can be controlled independently in one wind park including a plurality of wind turbines. A significantly rapid reduction can be achieved. Compared to coordinated control of a wind park using a higher-level HPPP controller, the response time for reducing power generation performed by the method described above is significantly shorter. Therefore, according to the method described above, the reliability of operation of a large power plant including the wind park and the entire power transmission system can be improved.

  According to yet another embodiment of the invention, a) the change in the determined frequency is an absolute value of the change in the value of the determined frequency, and b) the predetermined threshold is pre-set with respect to the absolute value of the change. It is a predetermined threshold value.

  To explain this, there are two thresholds for this frequency, starting from the center frequency representing the power balance between the power generated by the wind park and the power transmitted to the AC power system, depending on the absolute value of the change. It is prescribed. This means that when the determined frequency reaches or exceeds the upper threshold, and when the determined frequency reaches or falls below the lower threshold, the power The reference signal is changed. In particular, as described above, if the determined frequency reaches the upper threshold or exceeds this threshold, the power reference signal is lowered, and similarly the determined frequency reaches the lower threshold. Or if it falls below this threshold, the power reference signal is raised. Both of these measures contribute to achieving a (power) balance between the generated power and the power transmitted to the power system via the transmission system.

  In other words, a change in the determined frequency (of the AC output voltage signal) can be caused by a change in frequency that exceeds the upper threshold or the lower threshold. In this case, a positive maximum frequency change is defined by the upper threshold value, and a negative maximum frequency change is defined by the lower threshold value.

  By defining a threshold value for the determined frequency, it is possible to bring about an advantage that the operation control of the wind turbine can be realized in a remarkably simple manner. As a result, power balance can also be maintained.

  According to yet another embodiment of the invention, the power reference signal is held constant within a predetermined allowable frequency range.

  In other words, a predetermined power imbalance corresponding to a predetermined allowable frequency range of the determined frequency will be accepted without changing the power reference signal. This can provide the advantage that the operation control of the wind turbine is remarkably simplified and as a result also very reliable.

  For example, the allowable frequency range can be defined by an upper frequency threshold and a lower frequency threshold.

  According to yet another embodiment of the present invention, a) the determined frequency change is a derivative with respect to time of the determined frequency, and b) the predetermined threshold condition is a derivative with respect to time of the determined frequency. Contains the upper limit for the value of. According to this, it is possible to bring about an advantage that an appropriate change in the power reference signal can be achieved at an appropriate time according to the obtained frequency change speed. In particular, if a remarkably strong and / or rapid frequency change occurs, the reaction can be carried out in a short period of time by the aforementioned operational control of the wind turbine. This can contribute to the extremely high stability of the power balance described above.

  In this regard, as will be appreciated by those skilled in the art, it is necessary to determine the frequency at at least two different times in order to calculate the derivative of the frequency of the AC output voltage signal supplied by the power converter with respect to time. There is. In other words, this means that it is necessary to carry out a further step of determining a further frequency of the AC output voltage signal supplied by the power converter, which was mentioned first. The frequency and yet another frequency are obtained at different times.

This will be explained in advance based on the absolute value of the derived frequency derivative, or i) the obtained frequency derivative and ii) the obtained frequency itself. A control procedure sequence can be initiated. Such a sequence could be
a) reducing the active power limit to a preset value over a predetermined set period; and
b) by raising the active power back at a predetermined set ramp rate until the wind turbine reaches a normal power generation level,
It can be operated.

  According to yet another embodiment of the invention, the power reference signal for the wind turbine is limited to a predetermined range.

  In other words, regardless of the magnitude of the frequency change, the allowable range for (the magnitude of) the power reference signal is limited.

  To explain this, according to this embodiment, the power reference signal (magnitude) is clamped to the upper limit of the specified range (if a strong frequency drop occurs) or Clamped to the lower limit (when a strong frequency increase occurs). Such clamping can provide the advantage that the operation control of the wind turbine becomes simpler and more reliable. In particular, it is possible to prevent uncontrollable operating situations from being caused by measurement errors by limiting or clamping the power reference signal.

  It should be noted here that when there is essentially no significant active power imbalance in the system due to the limitation or clamping of the power reference signal, the normal approach (ie the current position of the wind turbine rotor in the wind turbine) is used. Based on available active power generation defined by the speed of rotation and the current pitch angle of the blades of the wind turbine rotor), it will be possible to control the power reference of the wind turbine, thus simplifying the control .

  According to yet another embodiment of the invention, within a predetermined range for the power reference signal, the change of the power reference signal is the difference between i) the determined frequency and ii) the desired frequency. Proportionally, this desired frequency corresponds to an operating state with a power balance between the power generated by the wind turbine and the power supplied to the power system via the transmission system. This can provide the advantage that the above-described operational control of the wind turbine is extremely sensitive while being extremely simple.

  According to yet another aspect of the present invention, a method for controlling overall power generation of a plurality of wind turbines in a wind park is provided. According to this, each wind turbine includes i) a mechanical drive train, ii) a generator mechanically connected to the drive train, and iii) power conversion electrically connected to the generator. With a bowl. Further, in this case, a plurality of power converters are electrically connected to one common node of the power transmission system that connects the wind park to the power system. The method provided here further includes the step of controlling the operation of at least a part of the wind turbine, preferably the operation of all the wind turbines, by performing each of the methods described above. In this case, the frequency of the AC output voltage signal is obtained at a common node.

  The idea on which this aspect of the invention is based is that coordinated control of the entire wind park can be achieved efficiently and automatically, even if each wind turbine is treated as an independent or individual generator. is there. In particular, in implementing the above-described method of controlling the operation of wind turbines, each wind turbine (controller) operates in a role that plays a role in common to all wind turbines, i.e. to the power grid. Operates to optimize power transmission. In this regard, the inventor of the present invention has found that the frequency representing the power balance or power imbalance between the total amount of power generated by the entire wind park and the total amount of power received by the power grid is monitored by a common node. For example, the above-mentioned problem can be simply solved by an easy and effective method. According to the present invention, the power reference signal is adjusted based on the current frequency determined or monitored.

  When the power transmission system is a high-voltage DC power transmission system, the above-described method for controlling the entire power generation by a plurality of wind turbines can be particularly advantageous. If the high-voltage DC transmission system includes a rectifier for converting AC power supplied by a plurality of wind turbines into DC power supplied to the high-voltage DC transmission line of the high-voltage DC transmission system, Strengths are even more important.

  The common nodes mentioned above can be defined by way of example by a wind park and / or a bus bar of the transmission system. In this case, the power converters of a plurality of wind turbines may be directly connected to an appropriate AC power transmission cable of a bus bar wire. As another option, a plurality of wind turbine power converters may be connected to the bus bar indirectly, eg, via one or more power transformers. In particular, the at least one power transformer can be a so-called step-up transformer that raises the voltage of the individual AC power (and generates a current).

According to still another aspect of the present invention, the following wind turbine is provided. In other words, this wind turbine
a) a mechanical drive train comprising a wind turbine rotor with at least two rotor blades;
b) a generator mechanically connected to the drive train;
c) a power converter electrically connected to the generator;
d) a rotor blade adjustment system for adjusting the pitch angle of the rotor blade;
e) including a power converter and a wind turbine controller that controls the operation of at least one of the rotor blade conditioning system. In this case, the power converter includes: c1) an AC / DC generator side bridge that rectifies AC power supplied by the generator; c2) a DC link that receives the rectified AC power; and c3) DC of the DC link. And a DC / AC system side bridge that converts power into AC output power. The wind turbine controller is configured to implement the method described above for controlling the operation of the wind turbine.

  Similarly, the idea on which this aspect of the invention is based is that frequency fluctuations are caused by power imbalance at a given point in the transmission system connecting the wind turbine to the power system. If it is identified that the stated frequency has changed to or within a predetermined range, the power imbalance is at least partially reduced by changing the power reference signal for the wind turbine controller. be able to.

  In terms used herein, the wind turbine controller may be responsible for controlling both the rotor blade conditioning system and the power converter (particularly the DC / AC system side bridge of the power converter). In this regard, the wind turbine controller may be a single computing device or, alternatively, may be implemented by two different computing devices, in which case one computing device is The other computing device is responsible for controlling the operation of the power converter or the DC / AC system side bridge.

  Having said so far, embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims, whereas other embodiments have been described with reference to apparatus type claims. However, as will be understood by those skilled in the art from the above description and the following description, unless otherwise specified, in addition to any combination of a plurality of features belonging to one type of subject matter, Any combination of the above features, particularly any combination of claim features in the form of methods and claim features in the form of apparatus, is also considered to be disclosed herein.

  The above-described viewpoints and further aspects of the present invention will become apparent from the embodiments described below, which will be described with reference to the embodiments. Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

1 shows a power generation and transmission system including a wind park with a plurality of wind turbines according to one embodiment of the invention. The figure which shows the wind turbine of the wind park shown in FIG. The figure which shows the rectifier of the high voltage direct current power transmission system shown in FIG. A graph showing how a power reference signal that depends on a frequency shift is limited according to one embodiment of the present invention. A graph showing how a power reference signal modified in dependence on a frequency shift is limited according to yet another embodiment of the present invention.

DETAILED DESCRIPTION The illustrations drawn in the drawings are schematic. It should be noted that in the various figures, similar or identical elements or features are denoted by the same reference signs or different reference signs from the corresponding reference signs only in the first digit. It is attached. Elements or features already described with respect to previously described embodiments will not be described again in the following description to avoid unnecessary repetition.

  FIG. 1 illustrates a power generation and transmission system 100 that includes a wind park 110 with a plurality of wind turbines 120. In the embodiment described here, the electric energy generated by the wind park 110 disposed offshore is transmitted to the power system 195 disposed onshore via the AC system 160 and the high voltage DC power transmission system 170. .

  The wind turbines 120 are arranged in groups, and one bus bar 112 is assigned to each group. As indicated by an arrow on the left side of the figure illustrating the wind park 110, the number of wind turbines 120 connected to one bus bar 112 is not limited. Each bus bar 112 is connected to the AC system 160 via a circuit breaker 114, which will be described in detail later.

  The wind park 110 has a centralized wind park controller (WPC) 118, which is communicatively connected to each one of the wind turbines 120 via a control line. In the case of FIG. 1, these control lines are represented by broken lines in the wind park 110. For the purpose of avoiding obscuring FIG. 1, the broken line connecting the wind park controller 118 and the wind turbine 120 that does not belong to the uppermost branch is shown broken. Each end point of the interrupted portion is represented by a black circle. It should be noted that the control lines or corresponding data transfer via those control lines can be realized by a wired data connection or by a wireless data connection.

  Wind park controller 118 is sometimes referred to as a High Performance Park Pilot (HPPP) controller, which is above all individual wind turbine controllers (not shown in FIG. 1). Operates as a located controller. The wind park controller 118 can control the operation of the individual wind turbines 120 in a coordinated manner by managing the individual wind turbine controllers. In addition, via the control line to the individual wind turbines 120, the wind park controller 118 can collect operational information about the individual wind turbines 120 and transmit appropriate control signals to each unique wind turbine controller. be able to.

  Next, a possible structural design of one wind turbine 120 will be described with reference to FIG.

  The wind turbine 120 has a windmill rotor 222 attached to a drive shaft 228. The wind turbine rotor 222 has a hub (not shown), and a predetermined number of rotor blades, preferably three rotor blades 224, are attached to the hub. Each rotor blade 224 can be rotated by a rotor blade adjustment system 226 about its longitudinal axis for the purpose of adjusting the pitch angle of the individual rotor blades 224. According to the basic principle of wind turbines, the pitch angle is an important parameter for the mechanical power extracted from the wind power obtained as a whole.

  The wind turbine 120 further includes a generator 230, which includes a generator rotor 232 that is driven by a drive shaft 228. In this connection, the wind turbine 120 shown here is a so-called direct drive wind turbine 120, which is mechanically connected to the generator rotor 232 between the wind turbine rotor 222 and the generator 230. A gearbox that can be used to increase the rotational speed of another connected drive shaft is not connected. Of course, a wind turbine having a configuration with a gearbox may be used.

  The generator 230 includes a stator 234 having a winding system, and the stator 234 generates electric power, generally three-phase power. A power converter 240 is connected to the subsequent stage of the stator 234. The power converter 240 has a generator side (alternating current / direct current) bridge 242, which operates as an active rectifier that supplies power to a direct current (DC) link 244 during normal operation. The power converter 240 further includes a system side bridge 246 that converts the DC power of the DC link 244 into AC power. According to the embodiment shown here, this AC power consists of a three-phase current and is supplied to the step-up transformer 248. The output of the step-up transformer 248 is set to each bus bar 112 shown in FIG.

  The wind turbine 120 has a wind turbine controller 250 and is controlled by this controller. According to the embodiment described here, the wind turbine controller 250 has two controller parts, a converter controller 252 and a pitch controller 254. The converter controller 252 controls the operation of the power converter 240 (of the semiconductor switch), as indicated by the dashed line in FIG. The pitch controller 254 controls the operation of the pitch adjustment system 226, and this pitch adjustment system 226 plays a role of setting the blade pitch angle of each rotor blade 224 in accordance with the actual operating state of the wind turbine 120. .

  Returning to FIG. 1, the AC system 160 includes a bus bar 161, a power switch 162, and a switch 163. At the bus bar 161, the power collected by the bus bar 112 is collected. When the power switch 162 is closed, the AC system 160 is connected to a high-voltage DC power transmission system 170 described in detail below.

  According to the embodiment described here, the power generation and power transmission system 100 includes the auxiliary power transmission system 164. This system 164 has an auxiliary power transmission line or an umbilical AC cable 165, whereby an AC power connection between the power system 195 and the wind park 110 can be established as necessary. As already mentioned, power transmission via the umbilical AC cable 165 may be used to enable a reliable start-up procedure for at least some wind turbine 120 start-up phases of the wind park 110 to other wind turbines. May be needed if 120 power generations are insufficient.

  As shown in FIG. 1, the auxiliary power transmission system 164 includes a transformer 167 and a power switch 168, and this switch 168 is used together with the switch 163 to activate or deactivate the auxiliary power transmission system 164. be able to.

  Further, as can be seen from FIG. 1, the AC auxiliary power transmission system 164 is provided with a power measuring device 166 that measures the power transmitted from the power system 195 to the wind park 110. As shown in FIG. 1, by performing voltage measurement and current measurement using two lines connecting the power measurement device 166 to the umbilical AC cable 165, the corresponding power measurement is performed by a known method. Is done. The power measurements are transferred to the wind park controller 118, which takes into account the actual level of power delivered via the umbilical AC cable 165 when coordinating the operation of the plurality of wind turbines 120.

  The high voltage DC transmission system 170 includes a plurality (three in the illustrated embodiment according to the invention) of diode rectifier power modules 172, each of which includes a three-phase rectifier 180 and an individual three-phase rectifier 180. A phase transformer 174 is included. The diode rectifier power module 172 is used to convert the supplied AC power into DC power. These diode rectifier power modules 172 include one output terminal of the three-phase rectifier 180 in the upper diode rectifier power module 172 and one output terminal of the three-phase rectifier 180 in the lower diode rectifier power module 172. The DC power having the voltage Udc is generated between them.

  As already mentioned, according to the embodiment described here, the wind park 110 is arranged offshore. The same is true for the diode rectifier power module 172 and the power switches 162, 163. A high voltage DC transmission cable 175 is used to transmit the generated power from offshore to onshore. On-shore, the high voltage DC transmission system 170 includes an onshore DC / AC converter 176 and a transformer 178 that (when the power switch 179 is closed) transfers the resulting AC power. Supply to power system 195 with appropriate phase and appropriate amplitude.

FIG. 3 shows details of the rectifier 180. In contrast to an AC / DC power converter, which typically includes six controllable high power semiconductor switches, the rectifier 180 only includes a power diode 382, which is a passive power component. As can be seen from FIG. 3, the rectifier 180 has three bridges, each of which extends between the two output terminals. An output voltage U _DC is generated between these two output terminals. Each bridge includes a series connection of two power diodes 382. One phase of the three-phase AC power supplied to the rectifier 180 is added at an intermediate node (not shown) between the two power diodes 382 of each bridge.

  In the following, in order to understand the operation control method described in this specification, some information will be given. In this case, for example, the power balance between the received power and the transmitted power depends on the determined or measured frequency of the AC power output of the wind park generated at the bus bar 112 or the bus bar 161 shown in FIG. The power reference signal for the wind turbine 120 is adjusted so that it is at least approximately achieved.

  In conventional high voltage AC transmission systems, the basic AC frequency is an inherent balance between power generation and load due to the electromechanical characteristics of synchronous generators and their governors.

  In the case of the operation control method described here, if the active power generated is larger than the active power removed from the offshore AC system, the fundamental frequency in the offshore AC system increases, and vice versa. Wind turbine power converters have similar characteristics.

  During normal steady state operation of the entire power generation and transmission system, wind turbine operational control is used to effectively balance the generation of active power in the offshore AC system and the effective power consumption removed by the onshore system. Designed to operate to change the active power flow towards This, combined with being a low-speed frequency controller, means that if the power flow towards the land is not restricted, the frequency will be the set reference frequency, or at least approach this reference frequency. Means.

If active power transmission is limited or even prevented, for example, by failure of a high voltage DC transmission system, the wind turbine can no longer balance the available power available in the offshore AC system, The determined or measured frequency will change. In particular, for example, onshore “continuation of low voltage operation” (LVRT)
The frequency will increase due to the maximum power limitation resulting from the occurrence of this event. Similarly, the frequency will drop due to, for example, the minimum power limitation for wind park offshore isolated operation.

  The present specification proposes a solution to this problem, which imposes an active power limit on the active power reference in each wind turbine. That is, in this case, 1) the maximum limit is applied if the determined or measured frequency increases, and 2) the minimum limit is applied if this frequency decreases. Obviously, the maximum power limit will limit the generation of active power to less than what is possible with the available wind power, and the minimum power limit will reduce the wind turbine rotor speed of the individual wind turbine. Will do. Finally, individual wind turbines can even be disconnected from individual bus bars.

FIG. 4 shows one example of such a restriction. According to this figure
P is the value of the individual wind turbine power reference signal relative to the available active power (depending on the actual wind conditions).
Δf is the change in frequency relative to the frequency reference in the individual wind turbine.
P1, P2, and P3 are power reference setting values stored in the lookup table.
F-3, f-2, and f-1 are delta frequency setting values in a lookup table that defines the minimum active power reference, and f + 1, f + 2, and f + 3 are lookup tables that define the maximum active power reference. Is the delta frequency setting value.

FIG. 5 shows yet another example of the aforementioned limitations. According to this figure
ΔP is the value of the change in the power reference signal for the individual wind turbine relative to the available active power (depending on the actual wind conditions).
Δf is the change in frequency relative to the frequency reference in the individual wind turbine.
ΔP1 and ΔP2 are delta power reference set values stored in a lookup table.
F-2 and f-1 are the delta frequency settings in the lookup table that define the minimum active power criterion, and f + 1 and f + 2 are the delta frequency settings in the lookup table that define the maximum active power criterion It is.

  In this case, in the case of FIGS. 4 and 5, the limit is defined as a delta limit, that is, the power deviation relative to the available active power and the frequency relative to the set frequency reference. It is defined as a deviation. However, an absolute value or a combination of a relative value and an absolute value may be used.

  Next, yet another approach for controlling the operation of a wind turbine is presented. This approach relies on the time derivative of the determined or measured frequency. According to this approach, the failure of the high-voltage DC transmission system and / or the power system causing the collapse of the power flow can be detected by a high-speed and reliable method.

  Within the normal range of wind turbine operating conditions, the rate of change of power flow is generally limited to, for example, 20% per second, by a ramp rate relative to the power reference (signal) supplied to the internal wind turbine controller. The upper limit for the power change rate can be defined as a post-fault power recovery ramp rate, for example 200% per second. When an onshore power system failure occurs, the power flow through the high voltage DC power transmission system is disturbed, and the DC link voltage of the high voltage DC power transmission system increases. As a result, an effect of transiently reducing the power flow from the offshore system to the high voltage DC transmission system is exerted. As a result, each wind turbine responds by raising its frequency in an attempt to meet its local power criteria. In this case, all wind turbines in the wind park will do this at the same time, so the offshore frequency rises very rapidly and rises much faster than the expected offshore frequency change rate within normal operating range. .

  A similar situation is caused when an offshore failure occurs. In other words, in this case, the power flow towards the high-voltage DC transmission system is reduced and all wind turbines try to compensate for this and try to increase their frequency, resulting in significant frequency changes over time. (Df / dt) is caused.

  According to the operation control method described herein, this problem can also be at least mitigated, which can autonomously detect for each wind turbine that a significant disruption of power balance has occurred. This is possible by using a df / dt value exceeding a predetermined threshold as a mechanism. The resulting control action at each individual wind turbine will reduce the level of the internal power reference signal and control the operation of the wind turbine accordingly. In such a situation, the value of df / dt is used as a (power system) failure detection mechanism.

  Similarly, during a significant disruption of power flow outside the normal operating range, the power error within one wind turbine will exhibit characteristics similar to the df / dt detection mechanism. Thus, power error can be a similar indicator of power imbalance in offshore systems and can be utilized for wind turbines with the goal of allowing (automatic system) faults to be detected autonomously as well. it can. This power error can also have thresholds and duration characteristics, which are applied to the power error to increase noise immunity (power system) and detect faults, for example, transformer switching, filter Offshore interference associated with energization is prevented.

  It should be noted that the notation “having” does not exclude other elements or steps, and the use of the article “one” means that a plurality of expressions “having” is provided. It is not excluded. Elements described for different embodiments may be combined. Furthermore, reference signs in the claims are not intended to limit the scope of rights of each claim.

Claims (13)

A method for controlling the operation of a wind turbine (120), comprising:
The wind turbine (120)
i) a mechanical drive train (222, 228);
ii) a generator (230) mechanically connected to the drive train (222, 228);
iii) including a power converter (240) electrically connected to the generator (230);
In a method for controlling the operation of a wind turbine (120),
The method includes the following steps:
Determining the frequency of the AC output voltage signal supplied by the power converter (240);
Identifying whether the determined frequency has changed more than a predetermined threshold with respect to the previously determined frequency;
If the determined change in frequency is greater than the predetermined threshold, changing a power reference signal for the wind turbine (120);
Providing the modified power reference signal to a controller (250) of the wind turbine (120);
Controlling the operation of the wind turbine (120) based on the modified power reference signal.
A method for controlling the operation of a wind turbine (120). In one node of the power transmission system (170) that connects the power converter (240) with the power system (195), the frequency is obtained,
The transmission system (170) comprises a high voltage direct current (HVDC) transmission line (175),
The method of claim 1. The high voltage DC transmission system (170) includes a rectifier (180),
The method of claim 2. The high voltage DC transmission system (170) includes an auxiliary transmission line (164),
The auxiliary power transmission line (164) is electrically arranged in parallel with the high-voltage DC power transmission line (175), and connects the power system (195) to the node of the power transmission system (170).
The method of claim 3. Controlling the operation of the wind turbine (120) based on the modified power reference signal comprises:
Controlling the operation of the power converter (240), in particular, controlling the operation of the DC / AC system side bridge (246) of the power converter (240), and / or
Controlling the pitch angle of the blades (224) in the wind turbine rotor (222) of the wind turbine (120),
5. A method according to any one of claims 1 to 4. The change in the determined frequency is an increase in the determined value of the frequency,
The predetermined threshold is a predetermined upper limit for the obtained frequency.
6. A method according to any one of claims 1-5. The obtained change of the frequency is an absolute value of a change in the obtained value of the frequency,
The predetermined threshold is a predetermined threshold for the absolute value of the change,
The method of claim 5. Keeping the power reference signal constant within a predetermined allowable frequency range;
The method of claim 7. The change in the determined frequency is a derivative of the determined frequency with respect to time,
The predetermined threshold condition includes an upper limit value for the value of the derivative with respect to time of the obtained frequency.
6. A method according to any one of claims 1-5. Limiting the power reference signal for the wind turbine (120) to a predetermined range;
10. A method according to any one of claims 1 to 9. Within the predetermined range for the power reference signal, the change in the power reference signal is proportional to the difference between the determined frequency and the desired frequency, which is determined by the wind turbine (120 ) And an operating state having a power balance between the power generated by the power system and the power supplied to the power system (195) via the power transmission system (170).
The method of claim 10. A method for controlling the overall power generation of a plurality of wind turbines (120) in one wind park (110), comprising:
Each wind turbine (120)
i) a mechanical drive train (222, 228);
ii) a generator (230) mechanically connected to the drive train (222, 228);
iii) a power converter (240) electrically connected to the generator (230);
The plurality of power converters (240) are electrically connected to one common node of the power transmission system (170) that connects the wind park (110) to the power system (195).
In a method for controlling the overall power generation of a plurality of wind turbines (120) in one wind park (110), the method comprises:
12. Controlling the operation of at least part of the wind turbine (120), preferably the operation of all wind turbines (120), by performing the method according to any one of claims 1 to 11, respectively. Including
Obtaining the frequency of the AC output voltage signal at the common node;
A method of controlling the entire power generation of a plurality of wind turbines (120) in one wind park (110). In a wind turbine, the wind turbine is
A mechanical drive train (222, 228) comprising a wind turbine rotor (222) with at least two rotor blades (224);
A generator (230) mechanically connected to the drive train (222, 228);
A power converter (240) electrically connected to the generator (230);
A rotor blade adjustment system (226) for adjusting the pitch angle of the rotor blade (224);
A wind turbine controller (250) that controls the operation of at least one of the power converter (240) and the rotor blade conditioning system (226);
The power converter (240)
i) an AC / DC generator side bridge (242) for rectifying AC power supplied by the generator (230);
ii) a DC link (244) that receives the rectified AC power;
iii) a DC / AC system side bridge (246) for converting DC power of the DC link (244) into AC output power;
The wind turbine controller (250) is configured to perform a method according to any one of claims 1 to 11.
Wind turbine.

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